This invention relates to data transmission networks, and more particularly, to a fiber optic network having data feedback.
In an autonomous network every terminal is capable of hearing the information or data transmission of any other terminal in the network to determine when the bus is idle. For this type of network (i.e., autonomous network) the architecture inherently provides signal feedback so that each terminal hears its own transmissions. Thus, in autonomous networks, or in any network in which the architecture provides a wrap-around of data output on the bus back to the transmitting terminal's receiver (i.e., star, linear bus . . . ), no additional feedback apparatus is necessary to monitor the integrity of the data outputted onto the bus.
The present invention finds particular application in a non-autonomous fiber optic data network, and may be applied directly to aircraft flight controls.
Optical data transfer is a relatively new technology that is replacing copper wire data buses in some application areas. A simple tee connection can be utilized in a copper wire data bus to provide feedback of the data output from a terminal connected to the data bus. This is not physically possible in a fiber optic network because of the directional nature of light.
System wrap-around techniques have been utilized to monitor the integrity of data on an optical bus. With this technique, data output from a controlling terminal is received by slave terminals and decoded. A message indicating the integrity of the received signal is then transmitted back to the master terminal by at least one slave terminal. The system wrap-around technique results in relatively high system complexity in that many active components are required to implement this monitoring technique. The system wrap-around technique results in high bandwidth requirements on the fiber optic bus because information regarding the integrity of the received signal must be transmitted from one or more slave terminals back to the controller.
Thus there is a need for monitoring the integrity of optical data output onto a fiber optic data bus from a controlling terminal while minimizing the complexity of the monitoring scheme. The present invention provides a fundamentally different scheme for monitoring the data on the optical bus then heretofore mentioned.
The present invention uses passive optical couplers to tap off a percentage of the optical power, which is routed to the terminal's receiver. This implementation, therefore, requires no active components outside of the enclosure of the terminal to monitor the data bus. Further, the bus in the present invention is being monitored at the terminal's output rather than at the opposite end of the data bus, thus providing very reliable information of the data being output onto the bus by the terminal being monitored. Increased bandwidth requirements are not imposed on the bus to implement the monitoring technique because the slave terminals are not required to transmit back any information for the monitoring technique of the present invention to be realized.